Sulfur degassing process

ABSTRACT

A process is disclosed for removing hydrogen sulfide from liquid sulfur including: passing a liquid sulfur feed comprising liquid sulfur and hydrogen sulfide to a vaporizer; vaporizing at least a portion of the liquid sulfur feed in the vaporizer to thereby form a first vapor stream comprising gaseous sulfur and gaseous hydrogen sulfide; partially condensing the first vapor stream in a condenser to form a liquid product stream comprising liquid sulfur and a second vapor stream comprising hydrogen sulfide; wherein the liquid product stream has a lower concentration of hydrogen sulfide than the liquid sulfur feed.

The present invention relates to a process for the degassing of liquidsulfur. In another aspect, this invention relates to a process for theremoval of hydrogen sulfide from liquid sulfur using vaporizationfollowed by condensation.

Since the presence of hydrogen sulfide in liquid sulfur can causeserious safety and health problems, as well as downstream processingissues, there is an incentive to remove hydrogen sulfide from liquidsulfur.

Therefore, development of an improved process for effectively removinghydrogen sulfide from liquid sulfur would be a significant contributionto the art.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, a process is providedincluding the following:

passing a liquid sulfur feed comprising liquid sulfur and hydrogensulfide to a vaporizer;

vaporizing at least a portion of the liquid sulfur feed in the vaporizerto thereby form a first vapor stream comprising gaseous sulfur andgaseous hydrogen sulfide;

partially condensing the first vapor stream in a condenser to form aliquid product stream comprising liquid sulfur and a second vapor streamcomprising hydrogen sulfide; wherein the liquid product stream has alower concentration of hydrogen sulfide than the liquid sulfur feed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic flow diagram presenting an embodimentof the present invention.

FIG. 2 is a simplified schematic flow diagram presenting an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The liquid sulfur feed of this invention can be any liquid sulfur streamwhich comprises, consists of, or consists essentially of liquid sulfurand hydrogen sulfide. Most typically, the liquid sulfur feed isgenerated from a sulfur recovery unit wherein hydrogen sulfide iscombusted with oxygen to form gaseous sulfur and sulfur dioxide, andnon-combusted hydrogen sulfide is reacted with the sulfur dioxide toform additional gaseous sulfur which is eventually liquefied.

At least a portion of the liquid sulfur feed is vaporized in a vaporizerto thereby form a first vapor stream comprising, consisting of, orconsisting essentially of gaseous sulfur and gaseous hydrogen sulfide.Preferably, at least about 70%, more preferably at least about 80%, andmost preferably at least about 90% of the liquid sulfur feed isvaporized in the vaporizer. The liquid sulfur feed is preferably heatedin the vaporizer.

The first vapor stream is partially condensed in a condenser to form aliquid product stream comprising, consisting of, or consistingessentially of liquid sulfur and a second vapor stream comprising,consisting of, or consisting essentially of hydrogen sulfide. The liquidproduct stream has a lower concentration of hydrogen sulfide than theliquid sulfur feed. Preferably, the hydrogen sulfide concentration inthe liquid product stream is less than about 50 wt. % of the hydrogensulfide concentration in the liquid sulfur feed, more preferably lessthan about 20 wt. % of the hydrogen sulfide concentration in the liquidsulfur feed, and most preferably less than about 10 wt. % of thehydrogen sulfide concentration in the liquid sulfur feed.

The liquid sulfur feed is preferably vaporized at a pressure belowatmospheric, more preferably below about 3.0 psia, and most preferablybelow about 0.6 psia; and at a temperature between about 450° F. toabout 1000° F., and more preferably at a temperature between about 600°F. to about 950° F.

The first vapor stream is preferably condensed at a temperature betweenabout 250° F. and about 310° F., more preferably between about 260° F.and about 300° F.

A first embodiment of the present invention will be described withreference to FIG. 1.

Referring to FIG. 1, the liquid sulfur feed is passed to a vaporizer 100by line 102. At least a portion of the liquid sulfur feed in vaporizer100 is vaporized to thereby form the first vapor stream. Steam is passedto an eductor 104 by line 106. The first vapor stream is educted fromvaporizer 100, and into the steam passing through eductor 104, by line108 which connects eductor 104 with vaporizer 100 in fluid flowcommunication. The eduction of the first vapor stream thereby results ina pressure below atmospheric in vaporizer 100 and a lower hydrogensulfide partial pressure of the combination of the first vapor streamand the steam leaving eductor 104 by line 110. Preferably, the hydrogensulfide partial pressure of the combination of the first vapor streamand said steam leaving eductor 104 is less than 80%, more preferablyless than 60%, and most preferably less than 40% of the hydrogen sulfidepartial pressure of the first vapor stream leaving vaporizer 100.

Line 110 connects eductor 104 in fluid flow communication with acondenser 112, passing the combined first vapor stream and steam fromeductor 104 to condenser 112. The first vapor stream is partiallycondensed in condenser 112 to form the liquid product stream and thesecond vapor stream. The second vapor stream is removed from condenser112 by line 114, and the liquid product stream is removed from condenser112 by line 116. The liquid product stream has a lower concentration ofhydrogen sulfide than the liquid sulfur feed.

A second embodiment of the present invention will be described withreference to FIG. 2.

Referring to FIG. 2, the liquid sulfur feed is passed to a vaporizer 200by line 202. At least a portion of the liquid sulfur feed in vaporizer200 is vaporized to thereby form the first vapor stream. The first vaporstream is passed to a condenser 204 by a line 206 which connectsvaporizer 200 in fluid flow communication with condenser 204. The firstvapor stream is partially condensed in condenser 204 to form the liquidproduct stream and the second vapor stream.

Steam is passed to an eductor 208 by line 210. The second vapor streamis educted from condenser 204, and into the steam passing througheductor 208, by line 212 which connects condenser 204 with eductor 208in fluid flow communication. The eduction of the second vapor streamthereby results in pressures below atmospheric in vaporizer 200 and incondenser 204.

The second vapor stream, along with the steam, is removed from eductor208 by line 214, and the liquid product stream is removed from condenser204 by line 216. The liquid product stream has a lower concentration ofhydrogen sulfide than the liquid sulfur feed.

The following example is provided to further illustrate this inventionand is not to be considered as unduly limiting the scope of thisinvention.

EXAMPLE

In six separate experiments, liquid sulfur feeds containing hydrogensulfide were vaporized and condensed, forming liquid product streams.The results are shown in the Table below, and demonstrate theeffectiveness of the present invention in lowering hydrogen sulfideconcentrations in liquid sulfur.

TABLE Liquid Liquid Liquid Sulfur sulfur Sulfur Feed H₂S VolatilizationCondenser Product Feed Flow Conc. N₂ Flow Temp Temp H₂S Conc. g/min ppmmL/min ° F. ° F. ppm 0.436 ^(a)390 ± 25 10 932 275 11.6 0.954 ^(a)390 ±25 10 932 275 16.0 1.54 ^(a)390 ± 25 10 932 275 21.8 1.63 ^(a)390 ± 2510 932 275 18.4 1.01 405 10 932 275 15.7 0.99 405 10 932 275 16.5^(a)These four experiments were performed during a continuous flowperiod where the feed H₂S concentration was reduced from 408 to 373 ppmover the course of all four measurements.

While this invention has been described in detail for the purpose ofillustration, it should not be construed as limited thereby but intendedto cover all changes and modifications within the spirit and scopethereof.

1. A process for removing hydrogen sulfide from liquid sulfurcomprising: passing a liquid sulfur feed comprising liquid sulfur andhydrogen sulfide to a vaporizer; vaporizing at least a portion of saidliquid sulfur feed in said vaporizer to thereby form a first vaporstream comprising gaseous sulfur and gaseous hydrogen sulfide; partiallycondensing said first vapor stream in a condenser to form a liquidproduct stream comprising liquid sulfur and a second vapor streamcomprising hydrogen sulfide; wherein said liquid product stream has alower concentration of hydrogen sulfide than said liquid sulfur feed. 2.The process of claim 1 wherein said liquid sulfur feed is vaporized at apressure below atmospheric.
 3. The process of claim 1 wherein thehydrogen sulfide concentration in said liquid product stream is lessthan about 50 wt. % of the hydrogen sulfide concentration in said liquidsulfur feed.
 4. The process of claim 1 wherein the hydrogen sulfideconcentration in said liquid product stream is less than about 20 wt. %of the hydrogen sulfide concentration in said liquid sulfur feed.
 5. Theprocess of claim 1 wherein the hydrogen sulfide concentration in saidliquid product stream is less than about 10 wt. % of the hydrogensulfide concentration in said liquid sulfur feed.
 6. The process ofclaim 1 wherein: an eductor is connected in fluid flow communicationwith said vaporizer and with said condenser; steam is passed throughsaid eductor; said first vapor stream is educted from said vaporizerinto said steam passing through said eductor, thereby resulting in apressure below atmospheric in said vaporizer and a lower hydrogensulfide partial pressure; and said first vapor stream and said steam arepassed to said condenser.
 7. The process of claim 6 wherein said liquidsulfur feed is heated in said vaporizer.
 8. The process of claim 6wherein said liquid sulfur feed is vaporized at a pressure below about3.0 psia and at a temperature between about 450° F. to about 1000° F.;and wherein said first vapor stream is condensed at a temperaturebetween about 250° F. and about 310° F.
 9. The process of claim 6wherein said liquid sulfur feed is vaporized at a pressure below about0.6 psia and at a temperature between about 600° F. to about 950° F.;and wherein said first vapor stream is condensed at a temperaturebetween about 260° F. and about 300° F.
 10. The process of claim 6wherein the hydrogen sulfide partial pressure of the combination of saidfirst vapor stream and said steam leaving said eductor is less than 80%of the hydrogen sulfide partial pressure of said first vapor streamleaving said vaporizer.
 11. The process of claim 6 wherein the hydrogensulfide partial pressure of the combination of said first vapor streamand said steam leaving said eductor is less than 60% of the hydrogensulfide partial pressure of said first vapor stream leaving saidvaporizer.
 12. The process of claim 6 wherein the hydrogen sulfidepartial pressure of the combination of said first vapor stream and saidsteam leaving said eductor is less than 40% of the hydrogen sulfidepartial pressure of said first vapor stream leaving said vaporizer. 13.The process of claim 1 wherein; an eductor is connected in fluid flowcommunication with said condenser; steam is passed through said eductor;said second vapor stream is educted from said condenser into said steampassing through said eductor, thereby resulting in pressures belowatmospheric in said vaporizer and in said condenser.
 14. The process ofclaim 13 wherein said liquid sulfur feed is heated in said vaporizer.15. The process of claim 13 wherein said liquid sulfur feed is vaporizedat a pressure below about 3.0 psia and at a temperature ranging betweenabout 450° F. to about 1000° F.; and wherein said first vapor stream iscondensed at a temperature between about 250° F. and about 31 0° F. 16.The process of claim 13 wherein said liquid sulfur feed is vaporized ata pressure below about 0.6 psia; and at a temperature ranging betweenabout 600° F. to about 950° F.; and wherein said first vapor stream iscondensed at a temperature between about 260° F. and about 300° F.